Re: [RFC 1/1] s390/cio: Remove uevent-suppress from css driver

[Cornelia Huck <cohuck@redhat.com>]

On Sat, 19 Dec 2020 07:33:16 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> I finally came around to test this. In my experience driverctl works for
> subchannels and vfio_ccw without this patch, and continues to work with
> it. I found the code in driverctl that does the unbind and the implicit
> bind (via drivers_probe after after driver_override was set).
> 
> So now I have to ask, how exactly was the original problem diagnosed?
> 
> In https://marc.info/?l=linux-s390&m=158591045732735&w=2 there is a
> paragraph like:
> 
> """
> So while there's definitely a good reason for wanting to delay uevents,
> it is also introducing problems. One is udev rules for subchannels that
> are supposed to do something before a driver binds (e.g. setting
> driver_override to bind an I/O subchannel to vfio_ccw instead of
> io_subchannel) are not effective, as the ADD uevent will only be
> generated when the io_subchannel driver is already done with doing all
> setup. Another one is that only the ADD uevent is generated after
> uevent suppression is lifted; any other uevents that might have been
> generated are lost.
> """
> 
> This is not how driverclt works! I.e. it deals with the situation that
> the I/O subchannel was already bound to the io_subchannel driver at
> the time the udev rule installed by driverctl activates (via the
> mechanism I described above).

That's... weird. It definitely did not work on the LPAR I initially
tried it out on!

However, I think removing the suppression still looks like a good idea:
we still have the "any uevent other than ADD will have been lost"
problem.